Does Low LED Power Density Affect Wear Resistance of Composite?

Research Article

J Dent App. 2015;2(2): 158-161.

Does Low LED Power Density Affect Wear Resistance of Composite?

Wagner Baseggio1, Flávia Pardo Salata Nahsan2, Cassiana Koch Scotti3*, José Carlos Pereira3 and Eduardo Batista Franco3

1DDS, MS, PhD, Professor at Paranaense University, UNIPAR, Cascavel, Paraná, Brazil

2DDS, MS, PhD, Professor at Federal University of Sergipe

3Department of Operative Dentistry, Endodontic and Dental Materials, Bauru School of Dentistry, University of São Paulo, Bauru, Brazil

*Corresponding author: Cassiana Koch Scotti, Octávio Pinheiro Brisola, 9-75 - Bauru - SP - Brazil - 17012-901

Received: September 09, 2014; Accepted: January 19, 2015; Published: January 21, 2015


Objective: This in vitro study assesses the initial curing light intensity effect on resin composite wear resistance.

Methods: Device Ultra blue IS (DMC), that it makes possible independent commands of power density and time was selected. Four different photo activation methods were investigated: Conventional A (CA: 600mW/cm2 X 40s), Conventional B (CB: 300mW/cm2 X 80s), Pulse-delay (PD: 300mW/cm2 X 3s 3 min wait 600mW/cm2 X 37s), and Soft-start (SS: 300mW/cm2 X 10s 600mW/ cm2 X 30s). Samples were prepared and stored in the dark for one week in distilled water at 37°C prior to simulated tooth brushing. The data were analyzed by statistical tests one-way ANOVA and Tukey.

Results: Ranking the abrasive wear values were as follows: CA>CB>PD>SS.

Conclusion: The findings indicated that a low initial curing light intensity did not compromised the abrasive resistance of the resin composite tested.

Keywords: Polymerization; Dental restoration wear; Composite resins


Polymerization shrinkage still remains an ultimate drawback and is a critical limitation of light-activated resin composites, once this process can disrupt the marginal seal between the composite and the tooth structure [1,2]. Polymerization shrinkage stress and its relieving mechanisms have become important research topics in dentistry and are positively correlated with irradiance, as well as the rate of stress force development, since in adhesive restorations the developing shrinkage stress of the setting material competes with the bond strength of adhesive to dentin [3].

Attempts have been made to reduce the stresses generated during polymerization shrinkage or minimize its effects. New methodologies of light application, so called “soft-start” methods, have been developed in order to overcome problems associated with polymerization. These strategies consist of a low-intensity initial irradiance followed by a stepped or ramped increase to higher-intensity irradiance, or a short and low-intensity irradiance pulse followed several minutes later by a longer exposure to high-intensity irradiance. These methods have been developed in order to decrease shrinkage stress and improve marginal integrity, without compromising the physical properties and quality of the restorations, allowing the restoration some freedom of movement between the cavity walls and the center of the contraction [4-6].

The purported reason for applying this new methodology in light curing, is to lengthen the pre-gelation phase by lowering the polymerization rate, thus providing more time for the resin composite to flow, relieve stress and, subsequently, result in an improved adaptation of the restoration [7,8]. Since contraction force is proportional to the degree of conversion, the exposure duration of the energy application sequence can be modified in order to promote similar degrees of conversion for proper light-curing of the resin composite, while trying to reduce or minimize the shrinkage stress during polymerization reaction [9]. This may be achieved with extended exposure times at low irradiance [5].

To date, the majority of studies have evaluated the so called “soft-start” polymerization technique in effectiveness to reduce gap formation or shrinkage stress, but fewer studies have evaluated its influence on polymer mechanical properties, such as wear resistance. Wear resistance is a very important property of the final resin composite posterior restoration and there is no consensus regarding which initial low-irradiation step should be applied.This study was outlined to verify the curing light intensity effects on wear resistance of a resin composite from a low irradiance LED light-curing unit.

Material and Methods

A hybrid resin composite (Z250, 3M-ESPE, St Paul, MN, USA) of A2 shade and a light-emitting-diode (LED) Ultra blue IS (DMC, Plantation, Florida, USA) were selected for this study. Ultra blue IS has an output wavelength range of 475 ± 15 nm and is programmed with exposure times of 20 to 40 seconds. The power settings or intensity are 300 and 600 mW/cm2. This allows for manual selection of any time and intensity combinations for the curing. Four different photo activation methods were investigated and are detailed in Table 1. The Conventional A method (CA) involves light irradiation at 600 mW/cm2 for 40 seconds. Conventional B method (CB) involves light irradiation at 300mW/cm2 for 80 seconds. Pulse Delay (PD) uses an initial low energy dose (300 mW/cm2) for 3 seconds followed by a three minutes waiting time and a final cure at high energy dose at 600 mW/cm2. The Soft-start (SS) method uses initial low-light intensity (300 mW/cm2) for 10 seconds immediately followed by final cure at high light intensity (600 mW/cm2) for 30 seconds. Light intensities were periodically checked with a commercial radiometer (100P/N- 150503, Demetron Research Corp., Danbury, CT, USA) before the start of each experimental session to ensure consistency of light output. Specimens were built using a steel mold (15 mm long x 5 mm wide x 4 mm deep), corresponding to the accurate measure of the existing space in the toothbrushing machine´s metallic bar for the setting of each specimen. A first portion of the resin composite with 2 mm of thickness and 7.5 mm of length was accommodated in the mold, representing half of the length and half of the height of the internal socket, corresponding to ¼ of its total dimensions. Three more portions were used for the specimen finalization (Table 1).

Citation: Baseggio W, Nahsan FPS, Scotti CK, Pereira JC and Franco EB. Does Low LED Power Density Affect Wear Resistance of Composite?. J Dent App. 2015;2(2): 158-161. ISSN:2381-9049